1. Field of the Invention
The present invention relates to a sheet antenna, which can be used for receiving or transmitting of electric waves. Particularly, the present invention relates to a sheet antenna, which can be used by adhering to surfaces of window glasses in motor vehicles and the like.
2. Description of Related Art
In recent years, it has been known to adhere sheet antennas containing an adhesive layer on surfaces of window glasses in motor vehicles in order to receive electric waves such as radio waves and television waves. The sheet antennas comprise a substrate sheet, a layer of antenna element composed of a conductive material formed on a surface of the substrate sheet and a adhesive layer formed on another surface of the substrate sheet.
However, there are some problems that the prior sheet antennas are poor in receiving or transmitting sensitivity of electric waves. Example of the problems is that images on television faceplates do not become visible when receiving television waves and therefore, it is difficult to watch the images. Accordingly, a sheet antenna having excellent receiving or transmitting sensitivity of electric waves is desired.
An object of the present invention is to provide a sheet antenna having excellent receiving or transmitting sensitivity of electric waves.
Extensive investigations undertaken by the present inventors directed to the object described above have led to the discovery that the receiving or transmitting sensitivity of electric waves can be increased by laminating the layer of antenna element composed of a conductive material and the carbon-containing layer on the substrate sheet.
The present invention, thus, provides a sheet antenna which comprises a substrate sheet, a layer of antenna element composed of a conductive material and a carbon-containing layer, the layer of antenna element and the carbon-containing layer being laminated on the substrate sheet.
In another aspect, the present invention provides a sheet antenna as described above, wherein an attaching layer is formed on a surface of the substrate sheet, in which the antenna element is formed, or the opposite surface.
In still another aspect, the present invention provides a sheet antenna as described above, wherein the attaching layer has removability and readhesiveness.
In further aspect, the present invention provides a sheet antenna as described above, wherein the attaching layer is an urethane elastomer layer having an elastic modulus at 100% elongation of not more than 6xc3x97106 N/m2 and a breaking strength of not less than 2xc3x97107 N/m2.
In furthermore aspect, the present invention provides a sheet antenna as described above, wherein a strong pressure-sensitive adhesive layer and a resin sheet are laminated on the substrate sheet, and the attaching layer is formed on a surface of the resin sheet.